alto rilievo vs relievo

alto rilievo and relievo both are nouns.

Word	Noun	Adjective	Verb	Adverb
alto rilievo	Yes	No	No	No
relievo	Yes	No	No	No

As nouns, relievo is a hypernym of alto rilievo; that is, relievo is a word with a broader meaning than alto rilievo:

alto rilievo: a sculptural relief in which forms extend out from the background to at least half their depth
relievo: sculpture consisting of shapes carved on a surface so as to stand out from the surrounding background

Other hypernyms of alto rilievo include embossment, relief, rilievo, sculptural relief.

alto rilievo (noun)	relievo (noun)
a sculptural relief in which forms extend out from the background to at least half their depth	sculpture consisting of shapes carved on a surface so as to stand out from the surrounding background